1. Field of the Invention
This invention relates to circuit interrupters having cause for trip indications, and has particular application to circuit interrupters having electronic trip circuits, such as sputtering arc and ground fault trip circuits in addition to thermal and magnetic trip devices.
2. Background of Information
Circuit breakers used in residential and light commercial applications typically house compact thermal and magnetic trip units in small molded housings of standardized dimensions designed for mounting in standardized load centers. The magnetic trip unit provides short circuit protection and the thermal trip unit protects against sustained overcurrents which cause excessive heating of the protected electrical system.
There is a growing trend toward also providing protection from ground faults in these small circuit breakers. Such protection is implemented by compact electronic circuits which are housed within compartments in the molded casing of the circuit breaker.
Recently, there has been interest in also providing protection against sputtering arc faults. Such faults occur for example when bared conductors, such as the strands of a braided extension cord, come into contact. The repulsion forces generated by the shorted current force the contacting conductors apart, momentarily interrupting the current. The conductors then return to the contacting position, such as through mechanical forces originally bringing them into contact, and the process is repeated. Such sputtering arc faults do not generate fault currents of sufficient magnitude to trigger the magnetic trip unit, or even the thermal trip. However, they can cause a fire in an appropriate environment.
Electronic circuits which detect sputtering arc faults have been developed, and have been incorporated into the small circuit breakers, typically, together with the electronic ground fault circuit.
Currently, there is no means for distinguishing between the causes of trip in such circuit breakers.